Why did Britain and France not declare war on the Soviet Union when the Red Army marched on Poland in September 1939?

Why did Britain and France not declare war on the Soviet Union when the Red Army marched on Poland in September 1939?

A Second World War memorial monument depicting Soviet soldiers. (De Agostini/W.B

A Second World War memorial monument depicting Soviet soldiers. (De Agostini/W.Buss)

The reason why Britain didn’t declare war on the Soviet Union is an intriguing one. Unknown to the general public there was a ‘secret protocol’ to the 1939 Anglo-Polish treaty that specifically limited the British obligation to protect Poland to ‘aggression’ from Germany.

When people questioned why Britain did nothing when the Red Army moved on Poland, the British government considered revealing the existence of the secret part of the agreement. However, they decided not to, Sir Alexander Cadogan of the Foreign Office explaining privately that to do so “would only provoke curiosity about the existence of similar secret protocols attached to other treaties…” An answer given in the House of Commons in October 1939 revealed only that the Poles had “understood” that “the agreement should only cover the case of aggression by Germany.”

From the outset, Soviet aggression was treated differently to German aggression. On a practical level this was because the British had already shown that they could not defend Poland against one aggressor, let alone two. But it was also because the mandarins in the Foreign Office considered the eastern borders of Poland somewhat ‘fluid’ – after all, they had only been fixed the treaty that ended the Polish-Soviet War less than 20 years earlier. Sir William Seeds, British ambassador to Moscow, wrote in a secret telegram on 18 September 1939: “I do not myself see what advantage war with the Soviet Union would be to us…” and that “our war aims are not incompatible with reasonable settlement [in Poland] on ethnographic and cultural lines.”

Behind the scenes, the British felt there was a clear balance to be struck between ‘morality’ and traditional, old-fashioned, national self interest. Yet, in the popular consciousness, this war is still considered almost a crusade against all evil.

Answered by: Laurence Rees, author of The Dark Charisma of Adolf Hitler (Ebury Press, 2012)

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